As one exemplary conventional in-vehicle device control system, a vehicular electronic key system (verification system) is disclosed in the following patent document 1. In this vehicular electronic key system, a control apparatus mounted in a vehicle performs checkup about a portable device carried by a user of the control apparatus by mutual radio communication, and controls the in-vehicle device based on a result of the checkup.
This vehicular electronic key system includes a smart security control apparatus mounted in a vehicle and a portable device carried by a user of the control apparatus. The smart security control apparatus transmits to the portable device a designation request signal, which designates a response frequency. When no radio signal is received within a predetermined allowable time period after transmission of the designation request signal, the smart security control apparatus transmits a designation request signal by changing the response frequency to a different frequency. The portable device selects the response frequency designated by the designation request signal and transmits to the smart security control apparatus a reception response signal of the selected response frequency. It is prevented that the response signal is not received because of jamming of the response signal. By thus making the radio communication to be less susceptible to influence of factors such as jamming, which disturbs radio communication, a control object can be operated normally.
However, in case of the system, which switches the communication frequency to perform the checkup again when the check result indicates an unsuccessful checkup, the frequency need be switched over until the check result indicates a successful checkup each time the checkup is performed even in a condition that the radio wave condition, in which the vehicle and the portable device are located, does not change. It is thus likely that the response characteristic is degraded due to an increase in the number of communications and time.